Field of the Invention
The present invention relates to a battery management technology, and more particularly, to a weighted least square (WLS)-based state of health (SOH) estimating system and method capable of easily estimating an aging state of a battery.
Description of Related Art
In general, electric vehicles or hybrid electric vehicles (hereinafter, referred to as “electric vehicles”) are driven using electric energy of a battery in an electric driving mode. Repeatedly charged and discharged, the battery, a secondary cell, is degenerated to have a degraded function, and thus, a degree of degeneration thereof is required to be evaluated.
An SOH, a parameter quantitatively representing a change in characteristics of battery capacity due to an aging effect, is a yardstick indicating a degree to which battery capacity has been degenerated. SOH is used to adjust battery charging/discharging capacity according to a replacement point of a battery and a battery usage term.
In fact, a change in characteristics of a battery capacity may be estimated by internal battery resistance and temperature. Thus, in the related art, internal battery resistance and battery capacity according to temperatures are measured in advance through charging/discharging experiment, measured capacity against initial capacity is relatively digitized to obtain a look-up table (LUT) for SOH mapping, and SOH corresponding to temperature and internal battery resistance is subsequently estimated.
Here, the internal battery resistance is difficult to directly measure during a battery charging/discharging process, so a technique for accurately measuring internal battery resistance is required.
Simply, internal battery resistance may be indirectly calculated by applying measured values of a battery voltage and a charging/discharging current to the Ohmng process, so a technique for accurately measuring inteas an error with respect to an actual voltage due to an IR drop phenomenon of a battery, and a battery current also has a measurement error, and as a result, SOH calculated using the Ohm's law has a significant error.
Another related art method for estimating SOH to reduce an SOH error is adding up charging/discharging currents of a battery to estimate a state of charge (SOC) of the battery, and estimating SOH using the estimated SOC. In this method, however, as the measurement error that occurs during a process of measuring a current is accumulated, accuracy of SOC used as basic data of SOH estimation is lowered with the lapse of time, resulting in a degradation of reliability of SOH estimation.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.